A set of keys is in the library.You can___the teacher for it.
I couldn’t work out this problem ________ my teacher helped me.
_________ my mother was washing clothes, my father was reading books.
When the first ______ came to the US, they were hungry as they have nothing to eat.
Spring is the best _______ of the year, because we can see lots of beautiful flowers.
I ________ the room yesterday, so it is not dirty today.